1. Field of the Invention
The present invention relates to a method of processing a substrate for removing surface roughness that occurs on a circumferential portion (bevel portion and edge portion) of a substrate to be processed, such as a semiconductor wafer, and films that adhere to the circumferential portion of the substrate to be processed to become stain sources.
2. Description of the Related Art
In recent years, along with the miniaturization of semiconductor elements and the high packing density of semiconductor devices, management of particles has become more important. As one of the big problems in managing particles, there is the problem of dust occurrence arising from surface roughness that occurs on bevel portion and edge portion of a semiconductor wafer (semiconductor substrate) in processes of manufacturing a semiconductor device. Herein, the bevel portion means a wafer portion having a slanted cross section at an end portion of the semiconductor wafer, and the edge portion means a flat surface wafer portion of around several millimeters from the bevel portion toward the internal side of the wafer.
For example, in a reactive ion etching (RIE) step of forming trenches (deep trenches) of a trench capacitor on a surface of an Si wafer, a by-product generated in etching adheres to the bevel portion and the edge portion of the wafer. Then, because this by-product works as an etching mask, thorn-shaped protrusions are likely to be formed on the bevel portion and the edge portion of the wafer (protrusions shown by reference numeral 25 in FIG. 3). In particular, when attempt is made to form an extremely large deep trench whose opening diameter is of a sub micron order, and whose aspect ratio is several tens, the above-mentioned thorn-shaped protrusions are apt to occur at the circumferential portion due to its process conditions.
Although the height of thorn-shaped protrusions varies with their positions on the wafer, it becomes nearly 10 μm at maximum, and these protrusions are broken at the time of transfer or processes of the wafer, and become causes of particles. Since such particles lead to the decrease of the yield of a semiconductor device to be manufactured, it is necessary to remove the thorn-shaped protrusions formed on the bevel portion and edge portion.
Conventionally, in order to remove such thorn-shaped protrusions and the likes, a chemical dry etching (CDE) method is employed. However, since the CDE method is of isotropic etching, and therefore, even if low thorn-shaped protrusions are removed completely, high thorn-shaped protrusions can not completely be removed, and some thereof are left unremoved. As a consequence, concaves and convexes according to the uneven height of the thorn-shaped protrusions are inevitably formed on the wafer. Dust easily collects in these concaves and convexes at the time of machine processing such as chemical mechanical polishing (CMP) to be carried out in later processes, which becomes a problem. Further, the processing time required for the CDE process per wafer is as long as normally 5 minutes or more. Accordingly, the CDE process leads to decline the throughput, and also increases raw material costs, which is a problem.
Further, in processes of manufacturing a semiconductor device, raw material films adhering to bevel portion and edge portion of a wafer become sources of stain. Therefore, it is required to remove the material films, however, in the CDE method, it is difficult to easily remove the material films.
Recently, in order to remove surface roughness that occurred on a circumferential portion of a wafer and films that adhere to the circumferential portion to become stain sources, a method of polishing the circumferential portion is carried out (as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-234314). In this method, a wafer is rotated and also a polishing member such as a polishing tape is contacted to a side surface of the wafer, thereby polishing the circumferential portion of the wafer. In this manner, it is possible to remove surface roughness that occurs on the circumferential portion of the wafer and films that adhere to the circumferential portion to become stain sources, in a short time.
However, this kind of method has the following problem. Namely, when a substrate side surface is polished, fine Si particles of the main component of the substrate, polishing particles of the polishing tape and the like scatter. Especially, when the substrate surface is hydrophobic, these particles adhere firmly to the surface. Therefore, even if physical cleaning of the substrate surface is carried out after completion of polishing process, particles can hardly be removed. Consequently, there is a problem on reliability of a semiconductor device to be manufactured. Furthermore, the method leads to the decline in yield.